The Hidden Forces Affecting Elevators in Tall Buildings

Author: Michael Muñoz | Senior Vice President, Design Services

Editor’s note: This is the third in a series of blogs sharing expertise from VDA’s webinar, Reaching New Heights: Tall Building Elevator Design.

For architects and developers, elevator design in a tall building is not simply a matter of adding more speed or capacity. As a building rises, forces that are easy to overlook early in design can influence the core layout, equipment performance, tenant experience, and ultimately the project economics. Longer suspension ropes add weight. Wind causes the building — and the elevator ropes within it — to move. High-speed cars push air through the hoistway, while temperature differences can turn the building’s vertical shafts into chimneys.

In our recent webinar, Reaching New Heights: Elevator Design for Tall Buildings, I joined experts from across the VDA family to discuss the codes, elevator strategies, and design considerations that shape tall and super-tall projects.

My talk focused on four physical effects that are manageable when addressed early but can become more difficult and expensive to resolve later. In this blog, I’ll explain those conditions and the decisions that can help keep the elevator system operating as intended.

How Tall Is Tall?

The word tall can be subjective, so it helps to begin with a common definition. The Council on Vertical Urbanism (CVU) defines a tall building, for this discussion, as one measuring at least 200 meters, or 650 feet, and a super-tall building as one measuring at least 300 meters, or 984 feet.

As height increases, the elevator system must contend with four conditions that should be evaluated early:

• Longer and heavier suspension ropes
• Greater building and rope movement
• Higher operating speeds and hoistway pressure
• Larger indoor-outdoor

Let’s take a closer look at each of these four conditions and what design teams should consider early in the process.

1. Conventional Suspension Ropes Have a Practical Travel Limit

In a conventional elevator system, steel ropes connect the car and counterweight and are suspended from a machine at the top of the hoistway. As the building becomes taller, those ropes become longer and heavier. At some point, the combined mass of the ropes, car, counterweight, and other suspended equipment reaches the practical capacity of the machine.

With current steel-rope technology, the practical travel limit is roughly 1,600 feet, although the exact distance depends on the system. A larger, heavier car may reach its limit sooner than a smaller, lighter one because total system mass is the governing factor. In buildings that exceed this range, passengers may need to transfer at a sky lobby and continue in a second elevator.

Alternative suspension technologies can extend that range. KONE UltraRope, for example, uses carbon fiber coated in a proprietary polymer rather than conventional steel ropes. Its lower weight can support travel distances approaching 1,000 meters, or 3,300 feet, nearly twice the distance of a conventional system. The reduction in suspended mass may also lower power consumption, which can make the technology relevant to some shorter, energy-conscious buildings. As with any specialized system, however, the potential benefits should be evaluated against the cost premium for the specific project.

2. Building Sway Can Become Elevator-Rope Sway

Tall buildings move in the wind, which means their elevator hoistways move as well. Because elevator components are suspended vertically, the ropes can begin to sway within the shaft. The concern becomes more serious when the natural frequency of the elevator system aligns with the natural frequency of the building. Under those conditions, the amplitude of the rope movement can increase until the ropes contact landing equipment, rails, the counterweight, or the hoistway walls.

A wind-tunnel study should therefore be completed early in concept design. Testing allows the structural and elevator teams to model expected building movement and identify the floors and operating conditions at which elevator performance may be affected.

Once the worst-case conditions are understood, the control strategy can include several mitigation measures:

• Limit how long an elevator can remain parked at certain floors
• Reduce operating speed during severe wind
• Temporarily remove cars from service
• Park cars at designated safe floors, discharge passengers, and remain out of service until monitoring devices confirm acceptable conditions

The objective is not to eliminate building movement, but to understand it and establish operating parameters that protect the system.

3. The Piston Effect Creates Pressure Inside the Hoistway

An elevator car moving through a hoistway behaves much like a piston moving inside a cylinder. As the car travels, it compresses the air above or below it and forces that air through available openings at the landings. The result may be audible whistling, movement in the door panels, and additional pressure on the door system. The effect becomes more pronounced as elevator speed increases.

Single-car hoistways are particularly susceptible because they provide limited space for air to move around the car. The design team should evaluate these options before relying on secondary mitigation:

• Use grouped hoistways or another core arrangement where possible
• Reduce elevator speed, recognizing that this may compromise Class A performance expectations
• Increase hoistway size to create more room for airflow, recognizing that this reduces leasable or sellable area

Where the core arrangement cannot be changed, pressure-relief paths may be introduced between separate hoistways. For example, through a horizontal duct connecting shafts across a corridor or an opening between back-to-back shafts. These solutions require careful coordination with the mechanical, electrical, plumbing, HVAC, and fire-protection teams. Because the hoistways are separate fire-rated enclosures, each connection requires a fire damper, or fused damper, so the shafts remain separated during a smoke or fire condition.

4. The Stack Effect Is a Whole-Building Issue

In a tall building, vertical shafts can behave like chimneys. The effect is often most pronounced during winter, when warm indoor air rises through the elevator hoistways and creates negative pressure at lower levels. When exterior or lobby doors open, colder air is drawn into the building and continues to feed the upward airflow. Unconditioned loading docks can intensify the problem if they are not effectively separated from the elevator core.

Occupants may hear air moving through the hoistways. In more severe cases, the pressure differential can prevent elevator doors from completing the final portion of their closing travel, which can take the elevator out of service.

The most effective response is coordinated building design, not an elevator-only fix. Early measures may include:

• Compartmentalizing the building
• Controlling vertical air pathways
• Using entrance systems such as doors at elevator lobbies or revolving doors at building entrances to help interrupt the pressure cycle

If the issue is addressed only after construction, the elevator solution may require high-horsepower door operators and high-torque closers at every landing. Those repeated costs can be significant and still do not address the underlying building condition.

Additional Considerations for High-Speed and Evacuation Elevators

During the webinar Q&A, we discussed several reference points for high-speed elevator design. The important thing to remember is that system capability is only part of the equation. We also have to account for how acceleration, changes in motion, and pressure changes affect passengers:

• Custom-engineered example: Shanghai Tower’s observation-deck elevators operate at approximately 20.5 meters per second, or 3,600 feet per minute; the elevators travel more slowly in the down direction to limit pressure-related discomfort, such as passengers’ ears popping
• Typical commercially available speed: Approximately 10 meters per second, or 2,000 feet per minute
• Typical acceleration: Approximately 2 meters per second squared, although specialized applications may reach 2.5 meters per second squared
• Typical maximum jerk: Approximately 3 meters per second cubed, because passengers tend to perceive jerk even more readily than acceleration

Occupant evacuation operation, or OEO, presents a different kind of design decision. Under the International Building Code, buildings over 420 feet may be permitted to reduce the number of egress stairs when evacuation elevators provide equivalent capacity. That can create a meaningful area benefit for a developer.

In practice, however, the decision also depends on local market expectations and occupant acceptance. In markets such as New York, many teams study the option but ultimately retain the additional egress stair. As a result, OEO remains a relatively uncommon choice despite its potential advantages.

Address These Conditions Early

The central takeaway is straightforward: these conditions need to be considered early. Rope weight, sway, piston effect, and stack effect are not isolated equipment issues. They influence the building core, structural design, mechanical systems, fire strategy, tenant experience, and project economics. Early coordination with elevator design experts give your team more options and reduces the likelihood of costly compromises later.

If you are planning a tall or super-tall project, VDA, GUNN Consultants, and D2E can help evaluate vertical transportation requirements in the context of the full building design. Our international group of elevator consultants draw on local experience from offices across the United States, Canada, the United Kingdom, India, and the UAE. Talk to an expert.

Keep Reading

Check out the first two blogs in our Tall Building series:

Tall Building Elevator Codes and Fire Safety: A Global Perspective by Paul Burns

Elevator Strategies that Make Tall Buildings Work by Eric Peterson

About the Author

Michael Muñoz joined VDA in 2006. As SVP of Design Services, he leads a team of engineers and vertical transportation professionals who support new construction and existing building projects across the U.S. and internationally. From early traffic analysis and system recommendations to construction drawings, specifications, RFIs, and shop drawing reviews, his team helps ensure elevator and escalator systems are thoughtfully designed, carefully coordinated, and aligned with each client’s goals. Follow him on LinkedIn.